The present invention relates to an apparatus and method for applying a thermoplastic powder to the internal threads of a fastener and other objects. More specifically, the present invention concerns a unique and novel spray nozzle which fits within the bore of a fastener and which selectively coats predetermined threads on the fastener.
In the application of thermoplastic powders to fasteners to create what are commonly referred to as self-locking fasteners and the like, among other things, an important consideration is to precisely apply the powder material to predetermined threads or locations on the fastener. Often, it is necessary or important to have a sharply-defined and clean lead thread on each end of the fastener so as to facilitate installation of the fastener. However, in smaller diameter internal fasteners such as M8 or smaller, the small diameter of the fastener with attendant reduced thickness makes it difficult to precisely apply the material and maintain a sharply-defined locking element with known nozzle configurations. In addition, it is necessary to control excess powder sprayed from the nozzle in the reduced working environment to prevent excess powder from adhering to and blocking the spray nozzle.
The present invention solves the above stated problems by providing a unitary nozzle that combines a powder collection port in close proximity to a powder application port. This nozzle is comprised of two elongated and engageable conduits. The first conduit has a passageway which is in communication with a powder supply and an air source. The second conduit telescopically engages the first conduit and has two passageways. The first passageway terminates in a discharge port and combines with the passageway of the first conduit to form a complete powder spray path which directs powder on to the threads of the fastener. The second conduit also has a second passageway in communication with a powder collection system and an inlet port through which excess powder is retrieved. To selectively coat predetermined threads on a fastener, the second conduit is first inserted into the bore of the fastener and then engages the first conduit. The conduit then moves axially within the fastener bore to coat predetermined threads on the fastener. Alternately, the fastener may also be moved axially with respect to the spray nozzle.
While the invention is particularly useful in processing small diameter internal fasteners, it is useful for larger sizes as well. Thus, one object of the present invention is to provide an apparatus and method which may be used to selectively apply thermoplastic powder to small diameter internally threaded fasteners and other small objects.
Another object of the present invention is to provide an apparatus and method which applies thermoplastic powder to predetermined threads on a fastener.
Yet another object of the present invention is to provide a method and apparatus which produces a sharply-defined patch and clean lead threads on a fastener.